This invention relates to methods and apparatus for atmospheric sampling and analysis of trace contaminants, and more particularly, the invention relates to such methods and apparatus which utilize gas-phase preconcentration interface systems.
The rapid and accurate monitoring of atmospheric contaminants, such as hazardous waste incinerator flue gas streams, is an important and necessary aspect, of air quality control programs. Such hazardous trace materials may be formed during the incineration of either hazardous or non-hazardous materials, or may pass through the combustion apparatus unchanged as a result of incomplete destruction of a hazardous material by the incineration process.
However, despite the advances made in the detection of substances in gas streams, frequent or continuous monitoring of such streams for highly toxic substances has not achieved the desired level of utility because of the difficulty encountered in obtaining samples, the laborious techniques frequently utilized to sample extremely dilute gas streams for a sufficient length of time to obtain a sample concentration sufficient for analysis, and the length of time necessary in certain procedures to prepare the sample for analysis. As a consequence of these difficulties, many exhaust or stack gas streams, such as those coming from municipal, industrial or hazardous waste incinerators, are only monitored periodically for the presence of toxic substances. For example, a hazardous waste incinerator may monitor for dioxin at certification and recertification (2-4 years) only. On the basis of this infrequent monitoring, the incinerator operator will make periodic adjustments in an effort to prevent toxic substance emissions from exceeding specifications, but system, feedstock, or process changes between such adjustments may adversely affect emission control. If, however, more rapid and less cumbersome methods of analysis were available, the incinerator operator could make more frequent adjustments.
While many systems have been used to sample and concentrate the components of a gas stream, the most commonly used systems are a bubbler or scrubber device where the gas is passed through a counter-current or stationary liquid, a solid sorbent such as charcoal, a suitable polymer and molecular sieves. Such methods, however, require additional steps to prepare the samples for analysis by the analytical instrument. Methods and apparatus for rapidly providing a reliably high degree of concentration of atmospheric contaminants in a sample stream which can be directly injected into an analytical instrument without requiring additional sample preparation steps would be desirable.
Efforts to monitor the content of a specific hazardous component (3-Quinuclidinyl benziloute or "BZ") in the flue gas of an incinerator being utilized to destroy the hazardous material are reported in "BezeTrog: An Effluent Sampling System for the BZ Incinerator Stack", for The Aerospace Corporation under Government Contract No. TOR-0084 (4712)-1 (1986); and "Theoretical Aspects of a Liquid Chromatographic Gas-Phase Interface", J. Chromatographic Science, Vol. 23, pp. 293-303 (1985). These publications describe a wetted-wall device in which the collection and concentration of trace quantities of BZ in incinerator flue gas was carried out in a concentration module comprising a small bore hollow cylindrical fluorocarbon polymer (Teflon) tube to achieve 8,000-10,000 fold concentration. While such a concentration increase is adequate for many substances which are present in a gas stream in the parts-per-million (ppm) range, further concentration is desirable, particularly when the hazardous substance is in the part-per-billion (ppb) range. In this regard, concentration increases to a range of at least 70,000-80,000 times the sample gas concentration of the hazardous trace substances would be desirable for rapid quantitative analysis of hazardous materials such as BZ in incinerator flue gases.